Communications cables consist of a plurality of electrically conductive wires which are bunched together, several such bunches being accommodated in an outer protective sheath. To join two such cables or even to join cables of different construction to one another, these bunches of wires have to be fanned out and joined to the wires of the other cable. The individual wires thus joined have to be insulated from one another, so that, in some cases, a much more bulky structure is formed. Since the insulation of the individual wires was opened, this structure has to be protected against the penetration of moisture or water. This is done by so-called cable fittings in the form of connectors consisting of a joint box and a plastics material accommodated therein.
The plastics materials used for hermetically sealing hollow articles, particularly cables, have to satisfy a number of requirements:
1. Their viscosity during processing should be low enough to enable the plastics material to penetrate readily between the bunches of wires and between the interconnected wires, even at low temperatures.
2. The self-curing of the material should take place quickly; the so-called pot life in the particular processing temperature range should be at least about 5 minutes.
3. The plastics material must show good self-curing properties at temperatures in the range from -10.degree. to 15.degree. C. so that the cables can be laid at any time of year.
4. The elasticity of the cured plastics material should be high to compensate temperature-induced changes in volume of the metal parts.
5. The adhesive properties of the sealing compound, i.e. its ability to adhere firmly to the constituent material of the joint box, to the insulating material of the individual wires and to the insulating material of the wires joined to one another, should be good.
6. High resistance to moisture and impermeability to water are also important requirements.
7. The cured plastics material should show high notch sensitivity, i.e. should crumble, so that, when the cable joint consisting for example of two joined half shells is opened, the plastic filling can readily be moved by hand without any need for tools.
8. In the cured state, the plastics material should show a high insulation resistance of more than 10.sup.11 cm on exposure to at least 1 kV/mm. The need for a high insulation resistance also applies after storage of the materials in water and various chemicals. The dielectric constant and the loss angle should be as low as possible. If the material comes into contact with acidic or alkaline liquids, it should remain serviceable for at least 36 hours at 38.degree. C. Finally, the plastics material should be resistant to the effect of diesel oil, fungi and microbes.
Hitherto known filling compounds based on various plastics materials, such as polyurethane for example, do not meet these requirements satisfactorily, if at all.